MPCC not doing its thing

[tileys]

It's early days getting my ASI 294MC Pro cam working with my 200mm F/4 reflector but something I have noticed is that simply screwing my Baader MPCC III coma corrector to the nose of the cam (into the low profile ring it comes with) and sliding into a couple of stacked extension tubes into the focusser, while it achieves focus, does not seem to resolve coma at the edges - like it did when attached to my Canon SLR previously.

This seems to be due to where in the image train I'm placing it. Short of trying just about every combination of adapters and tubes I have, has anyone got a similar setup and what did they find ?

cheers,

[The_bluester]

I presume the MPCC has a specific corrector to sensor distance like most others? The sensor is not nearly as deep in the camera body of an ASI294 as it is a DSLR. I am pretty sure it is 6.5mm back from the front face of the camera body (Not the end of the threads) where a DSLR is usually more like 40mm.

[tileys]

OK - thanks - that makes sense. Looks like I should introduce some space between the cam and the corrector then - will have to see if I've got something the right size - makes me wish I'd gone the fancy packaged version of the corrector now - I think that had some provision for adjustment.

It looks like the 11mm T2 ring plus the 21mm extender they supply with the 294 may give me something like I had with the EOS.

Will update with any solution as a ref for anyone with a similar setup.

[billdan]

The MPCC has to be located 55mm away from the sensor to work properly.

[tileys]

Thanks billdan - looks like the combination of the 21mm and 16.5mm tubes supplied will put me right on the money then with the 11mm T2 ring as well.

[ChrisV]

Yep, well thought out that ZWO supply those spacers. And there's two so one of them can be swapped out for their filter wheel if needed.

[tileys]

The supplied 21mm plus 16.5mm extensions together with the 11mm T2 ring and the 6.5mm of the sensor to front of body natural internal spacing of the 294 cam gave the spacing the MPCC needed - it screws onto the last extension - using the ZWO supplied connector ring internal inner and outer threaded ring that fits inside the extension and screws around the MPCC male thread.

Thanks.

One less thing to go wrong ;)